1. Field of the Invention
Aspects of the invention relate to a method of driving an organic light emitting diode (OLED) display device, and more particularly to a method of driving a time-division grayscale OLED display device that can prevent false contours and flickers from occurring at an interface between neighboring grayscales when displaying a moving image.
2. Description of the Related Art
A flat panel display device (FPD) is a display device that has largely superseded a cathode-ray tube (CRT) display device because the FPD is fabricated to be lightweight and thin. Typical examples of the FPD are a liquid crystal display device (LCD) and an organic light emitting diode (OLED) display device. Compared to the LCD, the OLED display device has a higher luminance and a wider viewing angle, and can be made thinner because the OLED display device does not require a backlight.
In the OLED display device, electrons and holes are injected into an organic thin layer through a cathode and an anode and recombine in the organic thin layer to generate excitons, thereby emitting light of a certain wavelength.
OLED display devices may be classified into a passive matrix type and an active matrix type depending on how N×M pixels arranged in a matrix are driven. An active matrix type OLED display device includes a circuit using a thin film transistor (TFT) to drive the pixels. A passive matrix type OLED display device can be fabricated using a simple process since anodes and cathodes are merely formed to cross each other to form a matrix of pixels in a display region. However, the passive matrix type OLED display device is applied only to low-resolution, small-sized display devices because it has a limited resolution, requires a high driving voltage, and its materials have short lifetimes. In contrast, in the active matrix type OLED display device, a TFT is provided in each pixel in a display region. Thus, a constant amount of current can be supplied to each pixel so that the active matrix type OLED display device can emit light with a stable luminance. Also, since the active matrix type OLED display device has a low power consumption, the active matrix type OLED display device can be applied to high-resolution, large-sized display devices.
Conventionally, an OLED display device displays a plurality of grayscales using a time-division method that divides a single frame into a plurality of sub-frames corresponding to bits of driving data and having different brightness ratios, and turns pixels on or off during the sub-frames according to the grayscale to be displayed. However, when sequential images, such as moving images, are displayed at a high speed, the emission times of neighboring grayscales become out of sequence due to the properties of human vision. Thus, false contours, which are generated by perceiving the images at a higher or lower grayscale level than the displayed grayscale, and flickering images (or flickers) occur.